dax turbo

iTrader: (1)

Other than; fuel pump, fuel pipe, filters being clogged, fuel regulator / connection to inlet manifold or fuel / surge tank pressurising is there anything else that could prevent fuel pressure rising as boost comes in? eg amal valve, ecu, chip, map sensor etc.? engine is 2wd cosworth running amal valve, standard fuel regulator, level 6 ecu

thanks in advance

P.S. this is driving me mad...

xr2wishy

iTrader: (2)

the only thing holding beack fuel pressure when it's coming on boost is the fuel pressure reg, fuel pump should be enough for 80psi, so you're fine up to 40psi boost lol!
so either your reg isn't right, of the manifold air feed is blocked or leaking.

tabetha

Easiest way is to just stick a vac pump on the pressure reg vac pipe, with a pressure gauge attached, then see the effect of losing/gaining vac has.
The fuel reg has TWO diaphragms, if the top one is holed and so not responsive to vac signal this will have the effect, you have, fuel won't leak as bottom one still ok.
I would also check exactly what vacuum you do have, inacurrate valve timing will lose a lot of vacuum, or if running silly lumpy cams may not develop much at idle.
tabetha

dax turbo

iTrader: (1)

thanks, i've plumbed in a fuel pressure regulator before the fuel rail which enabled the problem to be diagnosed. I've taken the vaccum pipe off the manifold and connected up to a bike pump. Pumping on this showed that up to around 7 bar at idle. Does this confirm that regulator upper diaphram is ok? How can i check vaccum pressure? i have a boost gauge plumbed in to another port on inlet manifold which should relect the pressure going to the fuel regulator shouldn't it (providing vaccum pipe not leaking)?

xr2wishy

iTrader: (2)

so at idle you're running 7 bar of fuel pressure?
i'm a little confussed.
quite simply, if you put some forced pressure in the regulator from the manifold air supply, then does the fuel pressure rise/afr enrichen?
if not then that is the problem right there, new regulator needed.
this is the only device that causes the fuel pressure to rise on boost.

dax turbo

iTrader: (1)

Just to clarify," I've taken the vaccum pipe off the manifold and connected up to a bike pump. Pumping on this showed that up to around 7 bar at idle." so yes fuel pressure increased from 3 bar at idle to up to 7 bar....does this confirm regulator is not the issue?

xr2wishy

iTrader: (2)

that does confirm it fella, so it's not the regulator nor the fuel pump.
why do you think the fuel pressure isn't rising on boost?
is it stuttering, it may just be the map being out.
only the manifold pressure effects the rise in pressure, as long as the fuel pump is fine, which your test shows.

Stu @ M Developments

iTrader: (12)

What are the symptoms that have led you to believe the pressure isnt rising?

Your advice is pretty good but it still could be the pump as there is no volume demand at idle.

dax turbo

iTrader: (1)

Stu,
Diagnosed when on torque of the devils rolling road. Guy next to the car noticed that fuel pressure wasn't rising when boost came in causing engine to run lean and misfire.

Agreed there's no demand at idle. Fuel pump is new bosch044. I've rewired pump following advice on the forum and checked voltage. I've also bypassed the relay and measured output direct from pump and before fuel rail which was identical at 2.2L in 30 secs from memory which seems in line with what it should be.

thanks

PGT

are you sure that the problem is the fuel pressure?

you don't say whether you have a pressure guage. if your wiring is poor then the pump might not be getting full battery voltage when its under load (i.e. when the reg is fed pressure from the manifold) thus low flow rate be interpreted as low pressure.

you can test the wiring by connecting a high power light bulb of 100 watts + (depending what pump you have) across the pump connections and seeing the voltage drop from the battery + to the pump +. it should be less than 1 volt if all is good.

PGT

bin my last post as i spent 20 minutes writing it thus overlapping!